SQL Query

Hi,

Need to write a query that does the following:

select F.col1, F.col2,
 case when  F.col3 = 1 Then XXX Else YYY End AS   P
from table F
left join (select T.col3 , T.m, T.n
              from tableT T
             ) as SecondTable  ON  secondTable.col3 = F.P
where ....
please note I need to compare the resultset of P (and not the F.Col3) against the T.col3


Thanks in advance